Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

948
FXUS63 KLOT 130050
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
750 PM CDT Tue May 12 2026

.KEY MESSAGES...

- Showers and a few isolated thunderstorms expected this
  evening, mainly along/south of the I-80 corridor.

- After a relatively cool Wednesday, temperatures will trend
  upward Thursday onward.

- The May 16 through 19 timeframe may feature several rounds of
  showers and storms in the general region.

&&

.UPDATE...
Issued at 750 PM CDT Tue May 12 2026

Minor updates to the near term forecast this evening, mainly
for pop trends and associated temp/wind impacts.

Early evening GOES vapor imagery depicts a deep mid-level
trough propagating across the upper Midwest early this evening,
with an embedded closed mid-level circulation over eastern Lake
Superior as well as a secondary vort wrapping around its base
across the MN/WI/IA/IL border region. 00Z surface analysis
places 1003 mb low pressure just north of Manitowoc, WI, with an
attendant cold front trailing southwest through far northwest
IL and eastern IA to the Kansas City area. An area of rain and
embedded heavier showers (but little/no lightning) was occurring
from west-central IL into northwest IN, within a region of
moisture transport/convergence on the nose of a 40-45 kt low
level jet. While surface dew points had risen into the low-mid
50s within the area of rain across the forecast area, low-level
moisture return was otherwise fairly limited which along with
poor low-mid level lapse rates associated with thick cloud cover
and rain-cooled boundary layer temps has yield only marginal
low-level instability (generally 250 J/kg or less).

For the remainder of the evening hours, additional shower and
isolated thunderstorm potential appears to be greatest along and
south of the I-80 corridor across the forecast area (and
farther north across eastern WI/LM), where the best moisture
transport and some MUCAPE will be focused. In fact, latest GOES
IR and radar trends indicate some new convective updrafts
developing in the VYS- JOT-GYY corridor. Severe weather threat
appears fairly minimal, though any stronger updrafts will be
capable of mixing some stronger winds to the surface. Can`t
completely rule out a few isolated showers farther north ahead
of the advancing cold front, though conditions appear much less
favorable north of I-80. All of the showers and isolated storms
will gradually shift southeast through late evening as the cold
front pushes through the area.

Gusty northwest winds behind the cold front have been
impressive across MN/northern IA with some 45-50 mph gusts noted
there. While it will be breezy overnight here, the loss of
deeper mixing after sunset should temper those higher wind
speeds as they arrive later tonight.

Ratzer

&&

.DISCUSSION...
Issued at 125 PM CDT Tue May 12 2026

Rest of Today:

The center of a low pressure system is currently over
southwestern Lake Superior and is moving eastward toward the
Upper Peninsula of Michigan. A cold front extends southward
through western Wisconsin and across central Iowa away from the
center of the low pressure system. Meanwhile, a narrow band of
showers with embedded thunder associated with low-level
isentropic ascent continues to fester across far northern
Illinois and southern Wisconsin. Ahead of the region of showers,
the boundary layer is deep and well-mixed with air temperature
and dew point spreads pushing 20 to 25 degrees. Southwesterly
winds continue to increase with recent gusts of 30 to 35 mph
noted near the Mississippi River. While upper-level clouds will
spread over the rest of the area through the afternoon as the
band of showers tries to shift southeastward, the continued feed
of warm air from the southwest will help high temperature reach
the upper 70s to around 80 in the next few hours. The exception
will be near the Wisconsin state line where showers will hold
temperatures some 10 to 15 degrees lower.

As the band of showers shifts southeastward through the area
this afternoon, attention will turn northwest toward the cold
front for signs of convective development. Cooling mid-level
temperatures ahead of the parent trough shifting atop a plume of
surface dew points in the upper 40s to around 50 will allow for
around 250 J/kg of MUCAPE to materialize ahead of the front by
late afternoon. Provided the instability materializes, largely
uncapped mixed profiles should allow for at least isolated but
probably scattered high-based but low-topped convection.
Relatively shallow echo depths should tend to limit the
development of large hail. With that said, the deep dry profile
beneath the cloud bases will promote locally gusty winds with
the heartiest precipitation cores. In all, cannot rule out a
locally damaging gust this afternoon, mainly between 6 and 9 PM.
Clouds will clear quickly behind the cold front overnight.

Not to be forgotten, still am expecting at least patchy but
possibly areas of blowing dust to develop this afternoon along
and south of Interstate 80 where gusty southwesterly winds will
overlap with working agricultural fields. A plethora of personal
weather stations are showing gusts in excess of 35 mph south of
I-80 right now, so would expect the blowing dust threat to only
increase through the afternoon. The threat should end toward
sunset as boundary layer winds relax and rain arrives.

Tomorrow:

Deterministic guidance remains in agreement that a secondary
upper- level trough (currently racing into central Manitoba)
will move into the Great Lakes tomorrow morning. While the
timing will not be favorable to maximize diurnal heating,
steepening low-level lapse rates (by virtue of low-level cold
air advection to lower 850mb temperatures toward 0C) should
support the quick development of a stratocumulus deck by mid-
morning. Provided the depth of the cloud deck grows sufficiently
deep, cannot rule out instances of sprinkles across the area
from mid-morning to mid-afternoon. Highs will be noticeably
cooler than today and in the upper 50s along the lakeshore and
in northwestern Indiana to the mid 60s across central Illinois.

Clearing skies and the slackening wind field will set the stage
for temperatures to tumble tomorrow night. While the outgoing
forecast will feature overnight lows in the upper 30s to lower
40s, would not be surprised if actual lows verify even colder
and in the low to mid 30s. If such temperatures were to verify,
frost would be a definite threat.

Thursday onward:

Toward the end of the week and into the weekend, a well-
advertised change in the upper-level pattern will take place
with predominant cyclonic flow along the US/Canadian border
turns to quasi-zonal and eventually southwesterly. The net
effect will be a notable upward trend in temperatures as well as
a return of regular opportunities for springtime thunderstorms.
Note that the pattern will be supportive of severe
thunderstorms in general region, particularly Friday through
Monday.

Borchardt

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 638 PM CDT Tue May 12 2026

Forecast concerns for the terminals...

- Scattered showers to linger across north-central IL this
  evening.

- Breezy west-southwest winds this evening with gusts upwards of
  30-35 kts. Winds then turn northwesterly behind a cold front
  after 03z.

- Period of MVFR ceilings Wednesday morning, before skies
  scatter back to VFR by midday.

- Breezy northwest winds on Wednesday with gusts around 20-25
  kts. A lake breeze is also forecast to move through ORD, MDW,
  and GYY Wednesday afternoon resulting in a northeast winds
  shift.


A surface low continues to drift across northern WI into the
southern UP and northern Lower MI this evening with a cold front
stretching from this low in WI into central IA. A plume of
showers has developed ahead of the cold front and continues to
slowly sag southward into north-central IL. While these showers
are expected to remain south of the terminals this evening,
there is still a low chance (15-20%) for an isolated shower to
develop along the cold front as it moves through northern IL and
northwest IN prior to 03z. Given the low confidence in new
shower development and lack of cloud growth on satellite have
opted to keep the TAFs dry.

Outside of the showers, winds this evening will remain breezy
out of the west-southwest with gusts generally in the upper 20
to lower 30 kt range through the evening. However, upstream
observations do show some locally higher gusts (upwards of 35+
kts) which may materialize over the terminals as the front gets
closer. If these gusts occur they should only persist for a
couple hours at most before they begin to wane. Once the front
moves through, winds behind it will turn northwesterly and will
decrease in speed with winds expected to be around 10 kts
overnight.

While generally VFR conditions are expected tonight, a plume of
MVFR clouds has developed in eastern MN with an upper-level
disturbance that will be pivoting into northern IL and northwest
IN Wednesday morning. Forecast soundings continue to show the
moisture depths to be rather shallow and with the lower clouds
not forecast to arrive until closer to daybreak confidence on
the longevity of MVFR ceilings is still somewhat low. Therefore,
have opted to include a TEMPO for a period of MVFR ceilings
(around 2500 ft agl) for a few hours Wednesday morning.
Regardless, any MVFR ceilings that do materialize should
scatter out by midday Wednesday as diurnal heating and
increasing winds erode the moisture plume resulting in VFR
conditions to close out the TAF period.

As mentioned, winds on Wednesday will once again be on the
breezy side with northwesterly gusts peaking around 20-25 kts.
Though, a lake breeze is forecast to develop Wednesday afternoon
and move inland through ORD, MDW, and GYY. Given the breezy
winds prior to the lake breeze development, confidence on when
exactly the lake breeze will move through is low so expect some
shifts in the forecast to occur as we get closer. Nevertheless,
winds will become more light and variable Wednesday evening as a
surface high moves overhead.

Finally, as the aforementioned upper disturbance pivots through
on Wednesday there is a non-zero chance (10-14%) for an
isolated sprinkle or two to get squeezed out of the mid-level
moisture plume. With the dry sub-cloud layer noted in forecast
soundings confidence on these sprinkles occurring is very low
and thus have foregone a formal TAF mention.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 7 PM CDT Wednesday for the IL
     nearshore waters.

     Small Craft Advisory until 1 AM CDT Thursday for the IN
     nearshore waters.

&&

$$

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